Field of the Invention
The present invention is concerned with the field of heating, ventilation and air conditioning (HVAC) and, more particularly, with a heating and/or cooling system which relies on a combination of air and ground source units.
Description of the Related Art
In the HVAC field, both air and ground source heating systems are known and can represent efficient heating and cooling systems under ideal conditions. As such ideal conditions are rarely obtainable or sustainable, and each of air and ground source heating systems will present certain advantages, HVAC installers typically rely on prevailing environmental conditions in determining the type of system that is best suited for a particular application.
In general, air source heat pump systems can be very efficient in areas where the outside temperature does not fall below 35° F. More specifically, under these warmer conditions, air source heat pump systems can extract a sufficient amount of ambient heat for use in heating the inside of a home or other building. Unfortunately, as many areas experience colder temperatures during certain periods of the year, an air source heat pump system will be subject to freezing and, therefore, is invariably used in combination with both a defrost system and an auxiliary heat source, such as an electric resistance heater element or an oil or gas burning system. Of course, it is also known to run an air source heat pump system in reverse for cooling purposes. Again, this operation can be efficient so long as the outside temperature is not excessive.
Ground source heat pumps are simply less affected by rapid changes in air temperature because their heat transfer takes place in the ground. Here the warmer and more consistent earth temperatures can provide an adequate heat exchange for both heating and cooling purposes. From this standpoint, ground source heat pumps can be even more efficient than air source heating systems and can be defrosted simply by shutting down for a requisite period of time. However, ground source heating systems are not without their drawbacks and are still typically supplemented by gas, oil or electric resistance heating units. In particular, ground source heat pumps are more susceptible to counterproductive outputs, high head pressures, damage to overheating subterranean coils, flow restrictions and compressor failures based on excessive run times in either heating or cooling modes of operation. On the other hand, as an air source heat pump generally has a sufficient supply of outdoor air for heat exchange purposes, long run times have little or no negative effect. Actually, the ability to operate with longer run times is also advantageous as the air source units can be sized smaller and can more effectively address humidification and other comfort issues.
In any event, both of these types of known systems have their advantages and disadvantages. Combination air and ground systems have been proposed but, to date, are not considered to be configured to operate at optimal efficiency. Therefore, a versatile combination heating and cooling system which could be effectively utilized under a wide range of environmental conditions, with the overall systems being capable of being factory built or retrofit, would be beneficial.